Partially epoxidized drying oils and derivatives thereof and their preparation



Unite This invention relates to the partial epoxidation of polyunsaturated drying oils having unsaturated (ethylenic) groups in isolated (non-conjugated) positions in either the cis or trans form. More particularly, it relates to the partial and selective epoxidation of drying oils containing linolenic acid, and to the resulting epoxidized products and crosslinked derivatives thereof which are useful in the preparation of coating vehicles.

Oils of the above type are referred to herein for convenience as containing linolenic and/ or other fatty acids. However, it should be understood that such references are intended to mean that the oils contain linolenic acid in its combined or esterified form rather than in its free acid form. This is in accordance with usual practice.

Oils which are used in the prepartion of coating materials such as oleo-resinous varnishes, alkyd resins, urethane oils and blown and bodied oils, are generally classified as drying, semi-drying and non-drying oils according to their drying characteristics. The drying characteristics are dependent upon the degree of unsaturation, usually expressed as the iodine number which is the weight percent of iodine the oil will absorb. According to the general classification, those oils having iodine numbers greater than 140 are drying oils, those having iodine numbers of 125 to 140 are semi-drying oils, and those having iodine numbers less than 120 are non-drying oils. The natural drying oils of the above type are triglycerides of mixtures, in varying proportions, of fatty acids which contain non-conjugated unsaturation. These are essentially linolenic, linoleic and oleic acids. Saturated acids such as stearic and palmitic acids, and minor amounts of other fatty acids may also be present. Such acids are conveniently referred to as drying oil fatty acids.

The drying oils, upon drying in air, set to films having only a slight tack in about 24 hours with normal drier concentrations, 0.5% Pb, 0.05% Mn and 0.05% Co as metals in the form of naphthenates, based upon the weight of the oil.

The semi-drying oils form films with a greater tack, but nevertheless show film forming characteristics. The non-drying oils are not film formers and usually become very tacky and viscous on exposure to air.

The film forming properties and the speed of drying of drying and semi-drying oils are functions of the degree of unsaturation, provided inhibitors or antioxidants are not present. Unsaturation of a definite amount is necessary to have drying properties and at least a minimum amount is needed to insure proper drying characteristics. The degree of unsaturation is also important in thermal polymerization reactions.

For the purposes of this invention, the process of drying a polyunsaturated non-conjugated drying oil should yield a film having, at the most, only a slight residual tack after drying twenty-four hours with conventional driers. An alkali refined linseed oil is used as a standard in this comparison.

It is known that oils which contain linolenic acid and linoleic acid with three and two double bonds, respectively, have different dried film properties. Thus, the oils with the greater degree of unsaturation dry faster and also exhibit, after the film has formed, what is known as after- States Patent yellowing. This is an objectionable change in color from an essentially white transparent type film to one which has a yellow cast or shade. It is for this reason that linseed oil paints are not satisfactory for interior use. Some soya bean oils contain less than 5% linolenic acid and exhibit a very low degree of after-yellowing. The literature is replete with references indicating that linolenic acid by virtue of the oxidation products which it forms on airdrying is responsible for the after-yellowing characteristics of oils in which it is present.

The blocking of an ethylenic group in unsaturated fatty acids may be achieved in many ways, e.g., by halogenation, hydrogenation, epoxidation, and in general by the use of reagents which will react with or add to the ethylenic structure. The blocking or saturation of an ethylenic group will reduce the functionality of the oil. However, we prefer to add to or replace the ethylenic group with another group essentially equally as reactive or functional. We have discovered that drying oils can be partially and selectively epoxidized to replace an ethylenic group with an essentially equal functional oxirane group so that the functionality of the oil is altered but not diminished. Moreover, we have discovered that the epoxidation can be effected so as to yield product oils which are still drying but are less subject to after-yellowing than the original oils.

It is, accordingly, an object of the invention to provide a method of selectively blocking one of the three isolated ethylenic groups in the linolenic acid component of drying oils which is responsible for the after-yellowing characteristics of drying oils, without eliminating the drying properties of the oils.

A particular object is to provide a method for partially and selectively epoxidizing polyunsaturated fatty esters of drying oil fatty acids.

Another object is to provide improved drying oils which are the products of such partial and selective epoxidation and in which the after-yellowing characteristics of the parent oils have been essentially eliminated or substantially reduced.

A further object is to provide reaction products of such partially and selectively epoxidized oils with cross-linking compounds that are reactive with the oxirane group, which reaction products are useful in the production of coating materials having improved properties.

Other objects will be apparent from the following description.

The objects of the invention are accomplished by the hereinafter described method for partially and selectively epoxidizing drying oils containing more than 5% by weight linolenic acid (in esterified form), by the resulting partially epoxidized oils and by the reaction products of such partially epoxidized oils with crosslinking compounds which are reactive with the oxirane group.

The drying oils which are useful for the purpose of the invention are those having polyunsaturated acids with isolated (non-conjugated) ethylenic groups and containing (in esterified form) more than 5% by weight of linolenic acid, which is 9,12,15-octadecatrienoic acid. By comparison, the semi-drying oils contain not over 5% or essentially no linolenic acid.

The useful oils include naturally occurring oils which are glycerol esters, examples of which are linseed, perilla, fish and other oils less commonly known and used in the coating industry. Such other oils are those derived from Euphorbz'a heterophylla, Salureja horterzs'is, Matiola bicornes, Reseola lutea and T halictrum species. Other useful drying oils are those made by esterifying polyols which are more functional than glycerol, i.e., having a hydroxyl functionality greater than three, with the drying oil fatty acids previously mentioned. Examples of such polyols 3 are pentaerythritol, dipentaerythritol, polypentaerythritol, sorbitol, polyvinyl alcohol and the like.

A drying oil of the above type is partially and selectively epoxidized in accordance with the invention by subjecting the oil to the action of hydrogen peroxide in the presence of acetic acid and an acid cation exchange resin in certain definite proportions. The amount of peroxide employed will be governed by the linolenic acid content of the oil and should be equal to at least 0.6 mole but not more than 1.3 moles of peroxide for every linolenyl group in the oil molecule. Preferably, from 1 to 1.1 moles of peroxide will be employed for each linolenyl group in the oil to be epoxidized. If more than the stated maximum amount of peroxide is used, the resulting product will be insufiiciently unsaturated to possess worthwhile drying properties. If less then the stated minimum amount of peroxide is used, the resulting selective epoxidation will not generally be sufiicient to reduce significantly the undesired after-yellowing characteristics of the oil. By so controlling the amount of peroxide employed, the epoxidized oil will still be sufiiciently unsaturated to retain important drying properties. However, in order to achieve a significant degree of selectivity of epoxidation of that double bond of the linolenyl group (believed to be the double bond in the 12,13 position), we have found it to be essential that the cation exchange resin be present in the reaction mixture in an amount equal, on a weight basis, to at least 0.29 part of resin (dry weight) per part of hydrogen peroxide (100% H The weight ratio of resin/hydrogen peroxide will generally range from 0.29 to 0.80, the preferred range being 0.40 to 0.60. Still higher proportions of the resin can be used, but are generally uneconomical. Following its use in an epoxidation, the resin can be separated from the reaction mixture and reused repeatedly in subsequent epoxidations. The amount of acetic acid employed, on a weight basis, should be equal to from 0.5 to 4.0 parts per part of hydrogen peroxide (100% H 0 the preferred amounts range from 0.75 to 2.0 parts of the acid per part of hydrogen peroxide.

Any of the commercially available aqueous hydrogen peroxide products containing from about 30 to 90% H 0 by weight can be employed in effecting the epoxidation. Use of solutions containing from about 45 to 70% H 0 is generally preferred.

The preferred cation exchange resins for the above purpose are the sulfonated copolymers of a monovinyl aromatic hydrocarbon such as styrene with from about 6 to 16% of a polyvinyl aromatic hydrocarbon such as divinylbenzene. In such resins, which are well known and widely used commercially, the sulfonic acid groups are attached directly to the aromatic nuclei of the resin structure. Other cation exchange resins such as those of the phenolic methylene sulfonic type can also be used. The resins should be employed in their acid form.

In general, the epoxidation will be carried out at temperatures from about 35 C. to 70 C., the preferred temperatures range from about 40 C. to 55 C. Higher temperatures cause excessive opening of the oxirane ring, while at temperatures below about 35 C., the reaction rate is too low to be practical.

The epoxidation technique of employing hydrogen peroxide and an acid cation exchange resin in the presence of acetic acid is described in E. I. du Pont de Nemours and Company Peroxygen Products Bulletin P6l-454 (April 1954) and in Greenspan et al. US. Patent 2,919,283. As there described, the technique is employed to effect as complete epoxidation as possible. Complete epoxidation is generally the desired goal of most epoxidation methods,

for example, those described in Neiderhauser et al. US.

Patent 2,485,160; in Findley et al. US. Patent 2,567,930; and in Wahlroos U.S. Patent 2,813,878. In contrast, the present method effects only a partial but selective epoxidation to obtain a product which retains valuable drying properties but is much less subject to after-yellowing than the original oil.

A linseed oil having an iodine number of 180, when fully epoxidized, will have an oxirane content of essentially 10%. Fully epoxidized linseed oils will not set to a film on exposure to air; they remain oily unless especial ly treated with curing agents. The oils prepared in accordance with this invention from 180 iodine number linseed oil will air dry to films provided the epoxidation has been controlled so that the oxirane oxygen content is not over about 3.4%. This means that not more than essentially one-third of the ethylenic groups have been converted to oxirane groups. Based upon iodine numbers, the partially epoxidized oil has properties about equivalent to a semi-drying oil and will form a film by normal air oxidation reactions. The present partially epoxidized oils which contain between 1.5% and 3.4% oxirane oxygen are useful film formers without further modification. In the case of linseed oil, this means that essentially about one to two of the six ethylenic groups present in this oil have been converted to the oxirane structure. Essentially, the 12l3 ethylenic bond has been completely saturated, i.e., epoxidized, with the balance of the oxirane groups distributed at other points. Because of the higher residual unreacted ethylenic unsaturation, the oils closer to the lower level oxirane oxygen content form better films.

The invention is illustrated by the following examples in which all parts and composition percentages are by weight unless indicated to be otherwise.

A number of epoxidations of alkali refined linseed oil having an iodine number of 180 were carried out employing in each instance 1000 parts linseed oil, 125 parts glacial acetic acid, 200 parts aqueous 50% hydrogen peroxide and suflicient of a cation exchange resin to provide the weight ratio of dry resin/ H 0 shown in the following tabulation. The cation exchange resin used was a commercial nuclear sulfonated copolymer of styrene with about 8% divinylbenzene. The resin was employed in the wet purchased acid form.

The resin and acetic acid were charged to an open reactor equipped with means for heating and cooling, such as a water bath, and with a stirrer and thermometer and means for slowly adding the hydrogen peroxide. After stirring for 30 minutes to thoroughly equilibrate the resin with acetic acid, the oil was added, followed by about 20% of the hydrogen peroxide. The temperature in the reactor was raised to about 40--45 C. and after about 30 minutes, the remainder of the hydrogen peroxide was added. The rate of addition was such that the reaction temperature did not exceed 45 C. This required about 3 hours. The reaction mixture was maintained under agitation at 45 C. for another two hours. After standing overnight, the supernatant layers were decanted from the resin. The oil layer was washed with water, dilute sodium bicarbonate solution, and again with water, then dried in vacuo.

. The following table shows the results obtained, including the relationship between the oxirane oxygen content,

the disappearance of linolenic acid and the resin/hydrogen peroxide ratio:

It is evident from the above results, that while the oxirane oxygen contents and iodine numbers were essentially the same for the epoxidized products of the three examples, the linolenic acid contents thereof decreased directly as the ratio of resin/hydrogen peroxide was increased. Thus, the preference for epoxidation of the linolenic acid component increased directly with the resin/ H 0 ratio. The oil products had colors of 3 and viscosities of C based on the Gardner scales.

Although the partially epoxidized oils of this invention are satisfactory film formers per se, it is preferable to use their oxirane functionality for further crosslinking reactions to form oil derived polymers. The following have been found to be useful crosslinking agents:

1. Dibasic acids or anhydrides with or without tertiary amine catalysts;

2. Triand tetra-functional acids;

3. Halides of non-metallic elements such as boron trifluoride as a gas or ether, amine or other complex thereof; and

4. Halides of silicon, phosphorous, and titanium.

The crosslinked reaction products of the partially and selectively epoxidized oils of this invention with any one of the types of reagents mentioned above, are different from prior products obtained by crosslinking prior fully epoxidized oils with these reagents. The prior oxirane containing products, either as epoxidized natural oils or their derivatives, contain oxirane oxygen greater than 3.5% as glycerol esters whereas 3.4% is the maximum for the present partially epoxidized oils. Usually, the prior products are reacted or crosslinked in moulds or in place, because of their short pot life. Since they contain little or no residual unsaturation, their conversion to the solid state is fixed and complete after the crosslinking reaction, with gelation and insolubilization occurring in a few minutes. Since our products still contain re sidual unsaturation after crosslinking the final film setting is by further air oxidation processes. The crosslinked products are stable, and remain in the liquid state almost indefinitely in solution when excluded from air. Thus, our products may be applied as varnishes or alkyd resins either as clear or pigmented coatings.

Some typical polycarboxylic acids or anhydrides that can be used as crosslinking agents are phthalic, fumaric, maleic, sebacic, trimellitic, pyromellitic, adipic, succinic, nadic, tetraand di-chloro-phthalic and chlorendic acids and anhydrides. The temperature of reaction and need for a catalyst are functions of the reactivity or acidity of the compounds mentioned. Generally, the acids or anhydrides which contain halogen and/or some free carboxyl are the most reactive.

In the preferred method of reacting the oxirane containing oil and the crosslinking anhydride or acid, both reactants are dissolved in a mutual solvent. Aromatic solvents such as xylene, ethyl benzene and isopropyl benzene are preferred but ethers and esters can be used. Concentration can vary from 50% to 90% nonvolatiles. Products containing the higher level of oxirane will yield more viscous solutions, hence a lower solids content may be preferable. The reaction temperature may vary from about 130 C. for chlorendic anhydride to 235 C. for orthophthalic anhydride. Any solvent employed should have a boiling point at least as high as the reaction temperature. Alternately, this same reaction may be conducted in a mass or bulk process without solvent. After the completion of the reaction, the crosslinked product may be dissolved in the solvents mentioned above prior to application.

In the above crosslinking reaction, one mole of the acid or anhydride reactant is equivalent to one oxirane group. When using an acid anhydride, somewhat less than the equivalent amount thereof will generally be employed, particularly when the oxirane oxygen content of the oil is 3% or greater, in order to prevent gelling. At lower oxirane oxygen contents, up to theoretical or equivalent amounts of the anhydride may be used. Thus, from about 60% to 100% of the equivalent amount of the anhydride or acid may be used, depending upon the oxirane oxygen content of the oil. The resulting crosslinked products are viscous oils having good film forming charf5 acteristics and are desirable drying oil vehicles which convert from liquid to solid by air oxidation.

When a catalyst is needed to initiate the above crosslinking reaction, it is preferred that the oil and anhydride or acid be heated with a tertiary amine such as triphenylamine, triethylamine, trimethylamine, or mixed alkylaryl amines with diiferent substitutent groups. The lower molecular weight amines are preferred. The amounts of these amine catalysts will generally vary between 0.1 and 4%, based upon product weight. Such catalysts in no way change the quality of the air-drying product.

The following examples will serve to illustrate the results of bulk polymerizations, in which varying amounts of chlorendic anhydride as crosslinking agent were reacted with partially epoxidized linseed oil products of different oxirane contents. The chlorendic anhydride and epoxidized oils of varying oxirane content were reacted at 130 C. in a vessel heated by means of an oil bath. The reaction time was 30 minutes. The final product was treated with driers such as 0.05% Co, 0.05% Mn and 0.5% Pb metal as naphthenates, and the film forming properties of the resulting products were observed. In the examples of the following table, 0.2% triethylamine was used to initiate the reaction.

Based upon amount: equivalent to the oxirane oxygen content.

In the following examples, phthalic anhydride was used as the crosslinking agent. The reaction temperature was 230 C. for 60 minutes with 0.2% triethylamine as the catalyst. The following table summarizes the results.

Percent Percent Example Oxiraue Oross- Acid Dried Film Oxygen linking Value Appearance in Oil Agent 1 6 2. 35 100 10. 0 Clear-hard.

3.19 6.9 Do. 8 3. 30 70 4.9 Do.

Based upon amount equivalent "to the oxirane oxygen content.

The partially epoxidized oils of the invention can also be crosslinked with boron trifluoride, or one of its complexes, such as with ether, acetic acid, amines and the like. In this case, the partially epoxidized oil is dissolved in mineral spirits or xylene and a dilute solution of the boron trifluoride compound, also in the same solvent, is added slowly and with constant agitation. The reaction is evident by an increase in viscosity and rise in temperature. The amount of boron trifluoride or its complex that is used with oils of varying oxirane content is quite critical. Too much boron trifiuoride causes gelation too rapidly. Thus, the preferred amount of boron trifluoride is from 0.1 to 1.6%, based upon the weight of the oil. Further, the concentration of the boron trifluoride in the dilute solution in which it is added should range from about 1.0 to 4.0%, based upon the weight of the solution.

The after-yellowing properties of the oil products of Examples 1, 2 and 3 were evaluated after they had first been crosslinked with phthalic anhydride as indicated by Examples 6 to 8 above. In the evaluation, the above oils were employed as the vehicles in paints prepared according to the formulation indicated below, and the resulting paints were tested as to their yellowing property and compared with corresponding paints containing safflower oil (which does not contain linolenic acid and does not yellow), linseed oil and a linseed fatty acid modified alkyl resin as control vehicles.

Weight per ga1l0n=12.75 #lgal. PVC=30%. Consistency=8085 KU.

Standard 2.5" x 12" white pine weatherometer panels were coated with two coats of the various paints prepared as indicated. After drying one week, the top halves of the panels were covered with aluminum foil and placed in a weatherometer for testing. All panels were exposed for 250 kilowatt hours excepting that for Example 11 which was exposed for 303 kilowatt hours.

After the above exposures in the weatherometer, the aluminum foil was removed from the panels. It was observed that the paints on the top halves of the panels showed yellowing, excepting the paints in which safilower oil and the oil product of Example 3 were employed as vehicles. Yellow ratings of '1 to 5 were assigned to the panels, a rating of 1 indicating no yellow and a rating of 5 indicating very yellow (most yellowing).

In a second series of yellow tests (North light tests) similarly coated panels were placed in an especially constructed dark box. The bottom halves of the panels were positioned in the bottom of the ventilated dark box, while the upper halves were outside and exposed to north light. Occasional examinations of the portions of the panels exposed to light and darkness were made. After weeks, the bottom halves of the panels were observed and assigned yellow ratings.

The results of the above tests are shown in the following tabulationz' Weatherometer North Light Example Oil Vehicle Test Yellow Test Yellow Rating Rating 3 3 2 2 1+ 1 1 1 nseed 4 4 14 Linseed AlkyL 5 4 We claim:

1. The method of obtaining improved oils having drying properties comprising reacting a drying oil containing at least 5% by weight of esterified linolenic acid with hydrogen peroxide in the presence of an acid cation exchange resin .and acetic acid, said hydrogen peroxide being employed in an amount equivalent to from 0.6 to 1.3 moles of H 0 for each linolenyl group present in the reactant oil, said cation exchange resin being employed in an amount corresponding to a weight ratio of said resin/hydrogen peroxide of from 0.29 to 0.80, and said acetic acid being employed in an amount corresponding to a weight ratio of said acetic acid/hydrogen peroxide of from 0.5 to 4.0.

2. The method of claim 1 wherein the reaction is efiected at a temperature of 35 C. to C.

3. The method of claim 2 wherein the cation exchange resin is a nuclear sulfonated copolymer of styrene and divinyl benzene.

4. The method of claim 2 wherein the reactant oil is linseed oil.

5. The method of claim 3 wherein the reactant oil is linseed oil.

6. A drying oil of the group consisting of (a) an epoxidized oil product of the method of claim 1 having an oxirane oxygen content of from 1.5 to 3.4% and (b) a crosslinked reaction product of said epoxidized oil product with a crosslinking agent which effects crosslinking by reaction with the oxirane groups of said epoxidized oil product.

7. A drying oil having an oxirane oxygen content of from 1.5 to 3.4% produced by epoxidizing linseed oil by the method of claim 2.

8. A drying oil produced by crosslinking the drying oil of claim 7 by reaction with chlorendic anhydride.

9. A drying oil produced by crosslinking the drying oil of claim 7 by reaction with phthalic anhydride.

References Cited by the Examiner UNITED STATES PATENTS 2,578,670 '12/1951 Carleton 260406 2,698,308 12/ 1954 Crecelius 2160-348 X 2,919,283 12/1959 Greenspan et a1. 26034S.5 2,949,441 8/1960 Newey 260348 2,976,265 3/1961 Pearce 260348 X 2,997,484 8/1961 Beavers et al. 260--348.5 3,042,687 7/1962 Chatfield 260-348.5

OTHER REFERENCES Du Pont Peroxygen Products Bulletin (April 1954).

Gunstone et al.: Chem. Soc. Jour. (London) (1962) pp. 3063-3068.

Swern et al.: J. Org. Chem. 22, p. 583-585.

Swern et al.: Chemistry and Industry, July 21, 1962, p. 1307-1309.

Suhara, Y.: I. Jap. Oil Chem. Soc. (1960), vol. 9, No. 11, pp. 607-611.

WALTER A. MODANCE, Primary Examiner.

JOHN D. RANDOLPH, Examiner. 

1. THE METHOD OF OBTAINING IMPROVED OILS HAVING DRYING PROPERTIES COMPRISING REACTING A DRYING OIL CONTAINING AT LEAST 5% BY WEIGHT OF ESTERFIED LINOLENIC ACID WITH HYDROGEN PEROXIDE IN THE PRESENCE OF AN ACID CATION EXCHANGE RESIN AND ACETIC ACID, SAID HYDROGEN PEROXIDE BEING EMPLOYED IN AN AMOUNT EQUIVALENT TO FROM 0.6 TO 1.3 MOLS OF H2O2 FOR EACH LINOLENYL GROUP PRESENT IN THE REACTANT OIL, SAID CATION EXCHANGE RESIN BEIN GEMPOLYED IN AN AMOUNT CORRESPONDING TO A WEIGHT RATIO OF SAID RESIN/HYDROGEN PEROXIDE OF FROM 0.29 TO 0.80, AND SAID ACETIC ACID BEING EMPLOYED IN AN AMOUNT CORRESPONDING TO A WEIGHT RATIO OF SAID ACETIC ACID/HYDROGEN PEROXIDE OF FROM 0.5 TO 4.0.
 6. A DRYING OIL OF THE GROUP CONSISTING OF (A) AN EPOXIDIZED OIL PRODUCT OF THE METHOD OF CLAIM 1 HAVING AN OXIRANE OXYGEN CONTENT OF FROM 1.5 TO 3.4% AND (B) A CROSSLINKED REACTION PRODUCT OF SAID EPOXIDIZED OIL PRODUCT WITH A CROSSLINKING AGENT WHICH EFFECTS CROSSLINKING BY REACTION WITH THE OXIRANE GROUPS OF SAID EPOXIDIZED OIL PRODUCT. 